Polyarylenes are of interest because the basic arylene unit has excellent thermal and chemical stability. Polymers containing only phenylene units have been described. One method for their preparation is the oxidative coupling of aromatic compounds, such as benzene, as disclosed in P. Kovacic, et al., Chem. Rev., 1987, 87, 357-379. This method involves a chemical oxidant such as cupric chloride and a Lewis acid catalyst, and in general results in insoluble polyphenylenes of uncertain structure. It is thought that polyphenylenes prepared by oxidation of benzene are branched and low in molecular weight.
Polyphenylenes of better defined composition have been reported by J. K. Stille, Die Makromolekulare Chemie, 1972, 154, 49-61. Stille found that the unsubstituted parent polyphenylene was insoluble in all solvents and did not melt. Phenyl substituted polyphenylenes, prepared by Diels-Alder cycloaddition of rather elaborate, and therefore costly, monomers, were soluble in organic solvents and could be processed into films. These phenylene substituted polyphenylenes appeared to have both para and meta catenation in the main chain, although the ratios of para and meta could only be inferred from the study of model compounds.
Substituted polyphenylenes have been disclosed by M. L. Marrocco, et al., in U.S. Pat. No. 5,227,457. Marrocco, et al., disclose rigid-rod (i.e. predominately 1,4 or para linked) polyphenylenes made soluble by the attachment of organic side groups. The side groups are chosen for a positive interaction with solvent, but are electrically neutral (uncharged) groups.
The chemical and physical properties, including thermal stability, glass transition temperature (T.sub.g), and dielectric constant (K), of substituted polyphenylenes depends on the solubilizing groups and the structure of the polymer backbone. It would be desirable to find polyphenylenes having lower K and higher T.sub.g, while maintaining good solubility and processability. It would also be desirable to provide polyphenylene compositions having well defined structures and high purity that may be produced from relatively low cost starting materials.